The present invention relates to variable volume dispensers and more particularly to such a dispenser having a dispenser tube through which the contents are expressed and a plug or closure member for the outlet end of the dispenser tube.
There are several types of variable volume dispensers known in the art. The present invention concerns those wherein the reservoir or body portion is deformable and has a dispenser tube extending up through the top of the bottle with a measuring chamber carried about the outlet end of the tube. In such a bottle, the deformable body portion is manually squeezed while holding the bottle in an upright position. This forces liquid up through the dispenser tube and into the measuring chamber. When the bottle is released any liquid above the level of the dispenser tube outlet is sucked back into the bottle. The bottle is then tipped to pour out the contents of the measuring chamber. With such an arrangement, the volume of liquid dispensed is reproducable. Also in such bottles of the prior art, the measuring chamber can be moved axially with respect to the dispenser tube to adjust the volume of liquid to be measured and dispensed.
One of the drawbacks of currently available variable volume dispensers of the type described is that they are not air tight. The open dispenser tube not only allows air, dust, and other contaminants to enter the bottle, but also allows volatile components within the bottle to escape. In a laboratory situation, dust covers can be placed over the unit to prevent the entry of contaminants into the bottle and to retard evaporation. However, such dust covers are not useful when the dispenser bottle is used in the field and will not prevent spilling or accidental discharge of the liquids as the bottle is being transported.